1. Field of the Invention
This invention relates to a sealed magnetic disk apparatus and, more particularly, to a magnetic disk apparatus in which a cover and base having steps at the periphery thereof are joined together via a seal.
2. Description of the Prior Art
A small magnetic disk apparatus used in many personal computers and workstations is very sensitive to gas and dust in the air. When they get in the apparatus, gas causes the apparatus (especially a disk) to be rusted, and dust causes the magnetic disk apparatus to be damaged because it gets in between the disk and a head floating on the disk. The small magnetic disk apparatus is therefore assembled in a clean room where gas and dust are very little.
In a conventional magnetic disk apparatus, the intrusion of gas and dust is prevented by sealing with a seal material. FIG. 1 is a simple example of a way of sealing for a small magnetic disk apparatus. In the magnetic disk apparatus, the intrusion of gas and dust is prevented by holding a seal 14 between the contact surfaces of a base 10 and a cover 12. Besides, in order to ensure the sealing, the four corners of the cover 12 and the base 10 are screwed down by bolts 16. So as to seal the periphery of the base 10 and the cover 12, the seal 14 is formed according to the outline of the periphery, for example, in a width of about 2 millimeters. The four corners of the seal 14 are curved inside so as to seal the insides of slightly swollen screw nut portions which are at the four corners of the base 10 and the cover 12. In the base 10, a hole 18 through which a shaft of a motor for rotating a disk is passed, is made. FIG. 2 shows an enclosure after sealing. Japanese Published Unexamined Patent Application (PUPA) 62-279586 discloses a magnetic disk drive apparatus which is provided with not only a first seal material corresponding to the seal 14, but also a second seal material between a cover and a bolt for fixing the cover to a base. As seen, a seal is one of important parts in a small magnetic disk apparatus.